1. Field of Invention
The invention relates to methods and apparatus for increasing the contact efficiency between a fluid and a liquid by a) inducing rotational movement in the liquid, and b) injecting very fine fluid bubbles into the liquid.
The method and apparatus can be applied to many fields, including purification of liquids and treatment of contaminated liquids by dissolving ozone into the liquid. The invention can also be used to treat any type of liquid with any type of fluid.
2. Description of Related Art
Establishing and maintaining efficient gas-liquid contact is essential for efficient mass transfer or absorption of a gas into a liquid. The gas can be diffused for many purposes, including purification and treatment of contaminated liquids with ozone.
The present invention generally relates to the field of water purification and treatment of flowable hazardous waste. Recent developments in water purification and treatment require ozone (O3) to be diffused into the liquid as part of the treatment process to destroy contaminants. There have long been various methods and devices for the treatment of biological and chemical contaminants in waste fluids. Large-scale water treatment facilities have been traditionally used for the treatment, removal, and processing of both human and low levels of industrial waste. With increased urbanization, these same water treatment facilities have been required to additionally treat complex mixtures of toxic and hazardous material from both private and industrial users. As a result, many of these same water treatment facilities are now unable to adequately treat the increased waste flow resulting in accidental or deliberate discharge of untreated material directly into the environment.
To combat the increased flow and more complex nature of current waste fluids, many wastewater utilities throughout the country require industrial generators of organic wastes high in biochemical oxygen demand (food waste, fats and oils, etc.,), recalcitrant xenobiotics (synthetic organic compounds foreign natural biological systems), heavy metals (Cd, Hg, Pb, etc.) and/or highly acid or alkaline pH to pre-treat their waste stream on-site prior to delivery to a waste water treatment facility. Although pre-treatment is required of many industries, liquid wastes generated by hospitals, medical facilities, medical examiners offices, healthcare offices, research facilities, nursing homes, food processing and animal handling facilities, diagnostic laboratories, veterinary clinics, analytical, chemical, microbiological, biotechnology and university laboratories in many instances are not required to pre-treat their collective wastewater stream even though this waste material is known to contain a variety of toxicogenic/mutagenic/ teragenic/carcinogenic chemicals and viable, infectious, or genetically altered microbial pathogens. Many of the current pre-treatment units presently in use are expensive to operate, require trained personnel to maintain and require the use of caustic and/or toxic chemicals or expendable filters and cartridges which must be disposed of as a hazardous substance.
Ozone has been used for more than sixty years for water treatment on the European continent. The role of ozone in waste fluid treatment may be classified as both an oxidant and a germicidal compound. There are at least four distinct recognized applications of ozone: (1) as a bactericide; (2) as a viricide; (3) as a powerful chemical oxidant; and (4) as a promoter of hydroxyl radicals when combined with ultraviolet radiation. The potent germicidal properties of ozone have been attributed to its high oxidation potential. Research indicates that disinfection by ozone is a direct result of bacterial cell wall disintegration. This is known as the xe2x80x9clysis phenomenonxe2x80x9d.
Ozone has several attributes in the treatment of waste fluids such as odor control, color removal, and iron and manganese removal. Ozone oxidizes inorganic substances completely and rapidly, e.g., sulfides to sulfates, and nitrites to nitrates. Of even greater importance is ozone""s capability of breaking down complex organic chemicals. Oxidation of organic materials is more selective and incomplete at the concentrations and pH values of aqueous ozonation. Unsaturated and aromatic compounds are oxidized and split at the classical double bonds, producing carboxylic acids and ketones as products. Ozone also exerts a powerful and bleaching action on organic chemicals, which contribute to the color removal in waste fluids.
Many of the treatment systems employing ozone are limited in their commercial application due to their relatively small scale and ability to deliver an adequate concentration of ozone sufficient for bacterial inactivation and chemical destruction. Typically these combined treatment systems have only been utilized for xe2x80x9cin-homexe2x80x9d domestic potable water treatment to remove taste and odor problems resulting from chlorination. As a result there has been considerable interest in improving ozone treatment systems and techniques to allow for the treatment of more complex waste fluids at higher flow rates, maximum efficiency and at minimal cost.
When treating a liquid, such as drinking water or contaminated water, by diffusing a gas, such as ozone, it has been recognized that the greater the area of interface between the water and the gas, the greater the amount of gas that will be dissolved into the liquid. Therefore, the goal is to put as many very fine gas bubbles into the liquid as is feasible. It has also been recognized that the amount of gas diffused into the liquid is in direct proportion that the time the bubble liquid interface is maintained. Therefore, an additional goal is then to keep the gas bubbles in the liquid being treated as long as possible before the bubbles reach the top of the reactor vessel (gas holdup). It has also been recognized that the dissolution occurs more efficiently if the bubbles move through the liquid rather than remaining relatively stationary in the liquid. This maintains the greatest concentration gradient at the gas-liquid interface. Therefore, an additional goal is then to have the gas bubbles move through the liquid over time.
Existing methods for establishing and maintaining the gas-liquid contact include a simple porous plate, punctured membranes, fans and turbines, to complicated motive jets mounted in reaction vessels to mix the gas and liquid. U.S. Pat. No. 5,720,905xe2x80x94Ho discloses a porous plate with openings between 0.2-2 mm to produce bubbles in liquid in a reaction vessel. Ho does not establish any means to reduce the size of the bubbles or increase the gas-liquid contact time. In Ho, the bubbles simply float directly to the surface of the liquid in the reaction vessel. U.S. Pat. No. 4,581,137xe2x80x94Edwards, uses a flexible membrane with plurality of minute punctures to discharge the gas in fine bubbles. U.S. Pat No.s 5,399,261xe2x80x94Martin, and U.S. Pat. No. 4,072,613xe2x80x94Alig, both disclose a mechanical stirrer blade mounted in the reaction vessel to breakup the gas bubbles to speed the dissolution of ozone into the liquid. U.S. Pat. No. 5,314,076xe2x80x94La Place, discloses turbines mounted in the reaction vessel to mix the gas bubbles in the liquid. The mechanical devices all require the expense of manufacturing the fans or turbines, increase the complexity of the system, and increase maintenance requirements by immersing mechanical devices in the liquid be treated.
U.S. Pat. No.s 6,139,755xe2x80x94Marte, and 4,162,970xe2x80x94Zlokarnik, both use complex nozzles to mix the gas and liquid. Marte discloses at least one jet nozzle to mix the gas and liquid, and produce an unstationary flow and cavitational flow to dissolve the gas. Zlokamik uses a single nozzle to disburse the gas into very fine bubbles, but no rotational flow is induced in the reaction vessel to increase the gas-liquid contact time and to move the gas bubbles through the liquid.
For the foregoing reasons, there is a need for a simple, efficient, non-mechanical apparatus, inexpensive to make and maintain, to enhance and control the amount of gas diffused in the liquid being treated.
The present invention is directed to an apparatus and method that satisfies the need described in the Background section. The object of the invention is to provide an apparatus and process for establishing and maintaining efficient and economical fluid-liquid contact. Efficient mass transfer or transport of a fluid into solution with a liquid is a function of the volume to surface area ratio of the bubbles, the contact time between the bubbles and the liquid, and the density gradient at the fluid-liquid boundary layer. The present invention can be used in a water purification system or hazardous waste treatment system. The present invention economically and simply provides maximum dissolution of a gas using readily available, low maintenance, and economical parts, and is compatible with existing systems.
The uses for the invention include establishing and maintaining contact between any type of fluid and a liquid. The fluid ejected through the apparatus into the reaction vessel includes liquids as well as gas. Use of the word xe2x80x9cgasxe2x80x9d in theses specifications and the claims represents all fluids, and does not limit the invention or the claims to only fluids in a gaseous state.
The invention involves an apparatus with nozzles that can be easily adjusted in size and orientation to optimize the gas-liquid contact time. The apparatus contains several nozzles or jets that cause very fine bubbles of the gas (or gas-liquid mixture) to be ejected into a reaction vessel. One or more nozzles are mounted at appropriate angles to direct the gas (or gas-liquid mixture) against the reaction vessel walls to further breakup the very fine bubbles. One or more nozzles are directed to discharge the gas (or gas-liquid mixture) such that the discharge moves rotationally around the vertical axis of the reaction vessel, thus inducing the gas bubbles and the liquid being treated to rotate around the vertical axis. The gas being drawn off at the top, and the liquid being drawn off at the bottom. Treatment efficiency is increased by maximizing contact time and increasing gas dissolution. The apparatus is mounted on a pipe or similar conduit in the reaction vessel. The pipe serves to deliver the gas (or gas-liquid mixture) to the apparatus and as a mount for the apparatus to locate it appropriately in the reaction vessel. The apparatus and the reaction vessel are incorporated into a system that includes a source for the gas, a recovery method for undissolved gas, a method for circulating the fluid to be treated, and a method for recovering the fluid after treatment. The system can also include a differential pressure injector, such as a Mazzei injector (Mazzei Injector Corp., U.S. Pat. No. 5,863,128) located outside the reaction vessel to pre-mix the gas and a portion of the fluid to be treated prior to ejecting through the apparatus into the reaction vessel.
As used herein, xe2x80x9cvery fine bubblesxe2x80x9d means bubble diameters less than 1 mm and the nozzle diameter, typically 6.75 mm. Very fine bubbles are preferably between 0.01 mm and 1.0 mm, and optimally between 0.01 and 0.10 mm. For increasing the contact efficiency, the smaller the bubble, the better. For example:
Bubble #1
Size (diameter) =1.0 mm
Volume =0.524 mm3 
Surface Area =3.143 mm2 
Bubble #2
Size (diameter) =0.1 mm
Volume =0.000524 mm3 
Surface Area =0.03143 mm2 
One thousand small bubbles (0.1 mm) can be made from the large bubble (1.0 mm). The small bubbles would have a total surface area of 31.43 mm2. This is 10 times the surface area of the 1.0 mm bubble. The small bubbles (0.1 mm) can theoretically ozonate 10 times as much water with the same amount of ozone, or theoretically introduce 10 times the ozone concentration into the same volume of water, i.e., given constant water characteristics, contact time and ozone solubility limits.
The invention also includes the process for dissolving a gas into a liquid by using fixed nozzles immersed in a reaction vessel to create very fine bubbles and rotational movement of the gas (or gas-liquid mixture).
An advantage of the invention described herein includes the use and arrangement of one or mores nozzles to produce rotational, noncavitational flow without using any mechanical device. The invention described herein also can be easily and economically adjusted to achieve a desired bubble size and contact time. These adjustments include but are not limited to changing the number, orientation, and size of the nozzles, by changing the gas pressure, by premixing the gas and the liquid before ejection from the nozzles, by changing the rate the liquid is withdrawn from the system.
The present invention relates to a process of and apparatus for treating dangerous biological waste, waste chemicals and other flowable waste to eliminate or render harmless, or inert, organic waste materials such as diseased human blood, cells and tissue, residual solvents used in cleaning human cells and tissue, and microorganisms for safe, charge neutralized and harmless release into conventional utility sewer systems, septic tanks and holding tanks, while meeting environmental standards established for these specific materials. This process and apparatus aid the user in achieving compliance with environmental statutes and regulations with maximum efficiency and at minimal cost.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, accompanying drawings, and appended claims.